In state-of-the-art integrated circuits, devices scale with each successive technology node, resulting in higher current densities per unit area. With higher current density, the copper wires in integrated circuits become more susceptible to electromigration which may cause the integrated circuit to fail.
Electromigration is the process by which voids are formed in a metallic conductor (e.g. copper/aluminum wires). At high current densities, a net atomic flux can be induced by a transfer of electron momentum to the atoms in the crystalline structure of the metallic conductors. The atomic flux may result in voids which can cause a circuit to break open or may result in hillocks (e.g., accumulation metal leading to shorts with adjacent metal lines). This process is accelerated by increased temperature and at high current densities, a signal line will heat due to Joule heating and may also induce a temperature increase in neighboring electric lines (and vice versa). In order to avoid deleterious effects the maximum temperature of the signal lines should be limited.